This invention relates generally to means and methods for removing unwanted layers from a surface and relates, more particularly, to the removal of such layers by cryoblasting processes.
Conventional cryoblasting systems utilized for removing unwanted layers, such as paint, from a surface commonly use compressed gas to accelerate solid bodies of cryogenic pellets, such as dry ice (carbon dioxide) pellets, toward a target area. Cryogenic pellets used in such applications provide an advantage in that the pellets evaporate (after use) and do not become part of the solid waste or are emitted as pollutants into the air and may, for these reasons, be preferred over conventional solvents or blasting grits used for similar purposes. Moreover, the acceleration of pellets in a venturi nozzle using compressed air in conventional techniques is highly inefficient.
Unwanted layers comprised, for example of epoxy and urethane paints of the type used on modern aircraft, are difficult to remove from a surface by conventional compressed air techniques unless air pressures used to accelerate the pellets toward the target area are elevated to very high levels. These high air pressure levels can severely degrade the pellets and produce a wide variation in the size and speed of the pellets impacting the target area which, in turn, can damage the substrate from which the unwanted layers are being removed. Moreover, the air/pellet stream may cause a rapid cooling of the target area, which cooling may adversely affect the removal of layers of material, such as paint. Still further, the compressed gas used in conventional techniques commonly must be cleaned, i.e., oil and water removed, before being used in some cleaning applications and normally requites relatively large filter systems to remove contaminants after use. It would be desirable to provide a cryoblasting system which circumvents the aforementioned problems normally associated with the use of compressed air in applications involving the removal of unwanted layers from a surface.
Furthermore, cryoblasting processes commonly require large quantities of high density cryogenic pellets. Materials such as argon and carbon dioxide which have high triple pressures, can be readily frozen by injecting the material (in a liquid state) into a chamber maintained below the triple pressure in a process commonly referred to as flashing. However, this process expands and freezes as a porous snow rather than a dense solid. To fabricate high-density pellets from the snow, extrusion machines are used to compress the snow at high pressure and force the material through orifices to produce solid sticks of ice which are chopped into pellets. If the extrusion pressure is high enough, the pellets can achieve a desired, full density.
It is an object of the present invention to provide a new and improved cryoblasting system and method for removing unwanted layers, such as paint, from a surface.
Another object of the present invention is to provide such a cryoblasting system and method which circumvents problems commonly associated with the utilization of highly compressed air for directing pellets toward a target area and which is more efficient than compressed air systems used for accelerating cryogenic pellets toward a target area.
Yet another object of the present invention is to provide new and improved means for accelerating pellets toward a target area in a cryoblasting process.
Still another object of the present invention is to provide a new and improved system and method for producing cryogenic pellets wherein the system and method are well-suited for large-quantity production of the pellets.
A further object of the present invention is to provide such a pellet-producing system and method which circumvents the need for extrusion machines and techniques used in conventional pellet production processes.